Blasting machine



1956 c. 0. MCKINNEY, JR. ETAL 2,763,813

BLASTING MACHINE Filed Sept. 30, 1953 CHARLES D. M KINNEY MILTON G. REITENOUR INVENTORS AGENT.

United States Patent BLASTIN G MACHINE Charles D. McKinney, Jr., Wilmington, and Milton G. Reitenour, In, New Castle, Del., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application September 30, 1953, Serial No. 383,158

Claims. (Cl. 315-205) This invention relates to a blasting machine and more particularly to a condenser type multiple shot machine whereby the ignition assemblies of large numbers of initiators may be simultaneously ignited.

In recent years there has been a trend toward firing increasing numbers of electric blasting initiators in a single shot. For a long time the standard blasting machine in the art has been the push-down or rack-bar, manually operated device which is limited to about 120 caps in a single shot. Where it became desirable to employ larger numbers of initiators in a single shot, it generally has been the practice to employ an engine driven generator or a service power line for the firing potential. Both of these techniques are inordinately complicated by the limited portability of the necessary equipment which, moreover, is simply not available in many cases.

More recently battery-operated condenser type machines have been developed which are capable of firing large numbers of caps. In these machines a charge is built up on a storage condenser which is manually or automatically released to the firing line. These machines have constituted a significant step forward in the art but still leave much to be desired from the standpoint of reliability, safety, and economy. Some of these machines have still lacked sufiicient power to fire several'hundred initiators. Others having sufficient power output have required such large and heavy batteries or hand generators for a power source that necessary portability has been sacrificed. Moreover, in all the prior condenser types there has been the possibility and danger of a condenser discharge to the firing circuit of a charge incapable of firing all the initiators. Such performance results in highly dangerous missed holes.

It is an object of the present invention therefore to provide an improved battery-operated condenser type machine which is capable of detonating simultaneously large numbers of electrical blasting caps whether connected in series, in parallel, or in series-'in-parallel. It is a further object of the invention to provide such a blasting machine which is portable, durable, relatively inexpensive, and simple to operate. It is an additional object of the invention to provide a blasting machine which is safe to operate from the standpoint of the blasting engineer and is eminently reliable in that partial shots due to discharge of insufiicient firing potential from the condenser are completely eliminated.

Generally described, the present invention is a blasting machine having in combination an input consisting of a source of low voltage D. 0; means associated with the input to interrupt the D. C. which comprises a reed vibrator, a charging switch connecting input and vibrator to the primary of a step-up transformer; a rectifier connected to the secondary of the transformer; acondenser connected to the output of the rectifier; a firing'switch which in its operating position connects the condenser to an output through a triggering circuit and disconnects the D. C. source from the step-up transformer, saidtriggering circuit comprising an interstage step-up transformer and a breakdown tube, said breakdown tube having a breakdown voltage higher than the maximum voltage to which the condenser can be charged.

In preferred embodiments of the blasting machine of the invention, a gas-filled glow tube is connected across the condenser to indicate the charge stored up therein. The rectifier may be a single rectifier tube or a plurality of such tubes arranged, for example, to form a bridge. High vacuum rectifier tubes or cold cathode tubes may be employed. Selenium rectifiers may also be employed and preferably the rectifier will be a bridge type selenium rectifier.

The presence of the triggering circuit is a special feature of the blasting machine in accordance with this invention which completely prevents discharging of the condenser through the firing circuit until adequate potential has been developed on the condenser to fire all of the initiators in the circuit. Thus, if a glow tube is connected across the condenser but functions improperly, a premature closing of the firing switch will not cause discharge of the condenser into the firing circuit. In like: manner, the condenser will not discharge prematurely if the firing switch is accidentally depressed prior to the build-up of the desired charge. As set forth above, the breakdown tube employed in the triggering circuit always Will have a breakdown voltage higher than the maximum voltage to which the condenser can possibly be charged, thus making it essential that a portion of the condenser charge be routed through the step-up transformer to generate a pulse high enough in potential to cause breakdown of the tube, thus allowing the condenser to discharge directly to the firing line. In order to conserve the firing potential built up on the condenser, it is preferred that a coupling condenser and resistor be disposed between the firing switch and the primary of the interstage step-up transformer, thus limiting the amount of the charge drained 01? from the condenser into the triggering circuit. It is also preferred that a resistor be connected across the secondary of the interstage step-up transformer and that this resistor be provided with an adjustable tap, thus permitting calibration of the triggering circuit to meet the demands of a particular breakdown tube.

Having generally described the invention, a preferred embodiment of a blasting machine in accordance therewith will be specifically illustrated in conjunction with the circuit diagram of the single figure shown in the drawing In the figure, a charging switch 1 is provided which has two sets of contacts 2 and 3 and 4 and 5, respectively. The switch is maintained in its normal or open position by spring 6 and in this open position connects contacts 4 and 5. In the closed or operated position the switch 1 connects contacts 2 and 3. A firing switch 7 is likewise provided with two sets of contacts 8 and 9 and 10 and 11, respectively. The switch '7 is maintained in the normal or open position by means of spring 12 and in this position connects contacts 10 and 11. In the operated or closed position the switch 7 connects contacts 8 and 9. A 6-volt drycell battery 13 is connected to vibrating reed 14 and magnetic coil 15 and to contact 2 of the charging switch 1 through contacts "til and 11 and switch 7 when the firing switch 7 is in the are connected across the primary 17 of the transformer 18. A bridge type selenium rectifier 19 is connected secondary 22 at by means of terminals 20 and 21 across terminals 23 and 24. A buffer condenser 25 is also connected across the secondary 22. The main storage confi'er 19"through' output terminals 27and"28i' Terminal 28 of the rectifier 19 is connected with contact 4 of the chargingswitch 1 through resistor 29, while contact 5 of the, charging switch 1 is connected to, terminal" 27 of'rectifier 19Jt0 discharge the condenser 26 when the charging switch 1 is in the open position as shown. A neon glow lamp 30 is connected across condenser 26 to indicate the charge on the condenser. Resistors 31- and 32 are provided to form a. voltage dividing network which determines-the potential at which the neon glow lamp' 30 will glow. The primary 33 of aninterstagc step-uptransformer 34 is-connected to contact'9 ofthc firing switch-7 through coupling condenser 35. A resistor-36 isconnected acrossthecondenser 35 to discharge condenser- 35 after switch-7 has been opened. A resistor 37 with an adjustable tap 38 is connected across the secondary 39 of theinterstage stepup transformer 34; The adjustabletap 38 of' the resistor 37 is connectedto-electrode. 40 of breakdown tube 4.1 through a: condenser 42. Resistor 43 isconnected across the condenser 42 to maintain electrode 4% at the neutral potential except when the tube is being triggered. Terminal 44 of breakdowntube-41 isconnected directly to positive plate of condenser 26 while electrode 45 of the; breakdowntube- 41 is connected to output terminal 46. Output. terminal 47. is connected directly to the negative plate of the condenser 26. A resistor 43 is connected across outputterminals-46tand47 to provide a discharge path for condenser 26 in the event the machine is fired wihout an initiator circuit connecting terminals 46 andy47.

The blasting machine shown in Fig. l operates as follows: The switch 1 being in its normal open position leaves contacts 2 and 3 open, thus isolating the battery 13 from the principal blasting machine circuit. With switch 1 in the-open position, contacts/4 and 5 areclosed, thus placing resistor 29 in parallel with the condenser 26. This removes anyresidual charge which may. be on thev condenser as'a result of'previous use.

By closing the switch 1, contacts 2v and 3. are brought intoconductive relationship and thelow potential of the battery 13 is applied on part of the primary 17 of the transformer'lhand across the magnetic coil 15 ofthe reed vibrator. The reed 14-is magnetically attracted towardvcoil ilfiand is drawn into engagement with contact 5t]. removes the attraction allowing. the reed 14' to swing back past its mid position to. engage the contact 49. Howevenas soon as engagementbetween contact 50 and reed 14 is brokemattraction is again built up causing the reed 14- to swing back and again engage contact 50. As long as the switch 1' is closed, this cycle is repeated continuously. The frequency of vibration may be controlled by the design of the natural period of the reed 14. Thus, as the reed 14 engages first the contactSO and then the contact 49 an alternating flux is setup in the primary Winding 17 of the transformer 18 and-an alternating voltage is induced across the terminals 23- and 24 of the secondary winding 22 of the transformer 18. The buffer condenser ZS'Which is connected across terminals 23 and 24 produces optimum wave form. and increases the life of the vibrator.

The alternatingvoltage produced across the secondary terminals 23 and 24 of the transformer 181is applied to terminals 2t and 21 of the selenium bridge rectifier 1 9.

When terminal 24 of the transformer 18 is of negative,

polarity, with respectto the terminal 23 of the transformer, electrons will flow from terminal 24 to input terminal 21 of bridge rectifier 19, to outputterminal27 of the rectifier, to storage condenser 26, to output terminal 28- of the'rectifier, to input terminal 20.0fthe rectifier, to terminal 23 of the transformer 18, and through the secondary windingof the transformer 1. to theterminal 24; By the nature ofthe, rectifier electrons; can

This engagement shorts: out the coil 15 and:

flow through it in only one direction. Therefore, for the other h'alf'of'the alternating voltage cycle terminal 24 of the transformer 18 becomes positive with respect to the terminal 23 and electrons then how from the terminal 23 to input terminal 20 of the rectifier to output terminal 27 of the rectifier, tostorage condenser 26, to output terminal 28 of the rectifier, to input terminal 21 of the rectifier, to terminalZd of the transformer and through thesecondary Winding to terminal 23.

It will be seen that for both halves of thcalternating voltage cycle the currentfiow with respect to the condenser 26 is' toward the negative plate and away from the positive plate of the condenser. Thus, electrons are flowingaway fromthepositive plate of condenser 26 causing a deficiency of electrons at the positive plate. At the same time, electrons are moving on to the negative plate of the condenser 26 causing a surplus of electrons at the negative plate. This process continues until'the potential-difference between the positive and mag ative-plates;of the condenser 26is equal to that across terminals-27- and 23 of therectifier 19,. When condenser 26 is charged, neon-lamp30 will glow. The exact potential at which lamp 39 lights depends on the values of the resistors 31 and-'32" which form a voltage dividing network'. The tube 30-willgive a visual indication thatthepotential on condenser 26 has reached the de sired and predetcrmined value;

Iii-order: torelease current to blasting initiators disposed: between output terminals 46 and 47, the firing switch 7"is'closed.' Theoperation of the switch 7 opens contactslO-and 11-and opens-the line from the battery- 1-3 to the center'tap 16 of the primary winding 17 of the transformer 18$ Contacts Sand 9 are closed to connect the condenser 26 to condenser and resistor 36. Condenserv35iacts as a coupling condenser between the con denser Ztiandfthe-primary 33 of the interstage transformer34 andallows only-an alternating voltage to pass.-

Resistort36eacts asa-bleederfor condenser 35' andis-of suflicientlyhigh value to allow only very limited direct currentrtotflow. therethrough; At the instant the firing switch 7tis closed; the-potential on condenser 35 rises sharply: fromtzeroitothe potential on the condenser 26. This'riserinpotential is a changing voltage and is readily passed by:condenserr35 onto the primary 33 of the interstagersteprupttransformer 34; This voltage rise or pulse PIOdllCBSiH. rising; flux in the primary 33 of the transformer 3.4;v which fluxsinduces a pulse in secondary winding 39j-of-;the transformer-34: The resistor 37 whichhas air-adjustable; tap: 3.8;:a1lows a pulse similar in shape but greater-in:amplitude:than that applied tothe primary breakdown, tube 41 tooutput terminal 46 and the detonators disposed-between the terminals 46, and, 47'. The resistance of resistor 48 is sufiiciently great that a negligibleamountgof thecurrent flowsthrough it.

By. varying, the.- position of 1 the adjustable tap- 38, of

the resistor. 37ythe-voltageofy the pulse applied to electrode;,40.. of the-breakdown tube 41 uponclosing of the firingnswitchfl can-be varied. The voltage of the pulse at. electrode, 40. is also dependent onthe voltage. on

condenser; 2.6,atthe instantqswitchfi isclosed. In practice; tap -38;-will preferably be-adjusted: so thatwhen condenser 26.-is-ful-ly charged-the voltage of the pulse on e1ectrode,.40-,isa-just,sufiicient to cause'ionization of thegas.in,.thebreakdown-,tube. When the condenser zfi is.

less than fully charged, a breakdown of tube 41 will not occur even though the firing switch 7 is closed and the blasting machine will fail to function. It will be seen therefore that the blasting machine of the invention cannot be operated until the condenser 26 is fully charged to the firing potential predetermined as necessary to fire all of the initiators in the firing circuit. Thus, rnisfires due to insuflicient firing voltage cannot occur unless the capacity of the machine is purposely exceeded.

In order to illustrate the performance of the blasting machine of the invention, the following examples are presented.

Example 1 Two thousand delay electric blasting caps were arranged in series-in-parallel. The caps were disposed in 50 series of 40 caps each with a IOU-ohm resistor added to each series. A blasting machine similar to that of the drawing and powered by a 6-volt dry battery was employed as a power source. All caps shot.

Example 2 Two thousand caps were arranged in series-in-parallel as in Example 1, except that instantaneous caps were mixed throughout the circuit. The 50 series were divided into 5 groups of series each. The first 10 series contained 40 delays each; the second 10 series contained 39 delays and one instantaneous cap; the third 38 delays and 2 instantaneous; the fourth 37 delays and 3 instantaneous; and the fifth 36 delays and 4 instantaneous. The same blasting machine was used as in Example 1. All caps shot.

Example 3 Although shooters are advised not to make unbalanced shots in the field, a badly unbalanced shot was made to test the capacity of the machine of the invention. Twenty-four series totaling 617 caps were arranged in parallel. The first series was a single delay cap while the second series was a single instantaneous cap. The remaining series were divided into 4 groups of 6 series each containing 10, 20, 35, and 40 delay caps, respec tively, with each series also containing from 0-5 instantaneous caps in addition to the delays. The delay caps varied in delay period from 0.8 to 3.7 see. A total of 617 caps were employed. The blasting machine of the previous examples was used. All caps shot.

As previously indicated, any desired battery of either the dry cell or storage type may be employed as the D. C. power source. The battery may be a single cell or may be composed of the requisite number of individual cells to produce the desired voltage. As the voltage is changed, of course, the characteristics of the vibrator and transformer will also be changed. As has been indicated, equivalent rectifying means may be substituted for the bridge rectifier illustrated in Fig. l which is made up of a number of low voltage selenium rectifiers connected in series. For example, high voltage selenium rectifiers may be connected in a bridge circuit or any commercially available rectifier may be substituted. Other types of semi-conductive rectifiers such as copper oxide, germanium, and silicon may also be employed as long as the components are made large enough to accommodate the voltage and current developed either by constructing a large unit or by wiring a number of small units together. Other rectifiers such as high vacuum rectifiers, mercury rectifiers, or cold cathode rectifiers may be used. The cold cathode type generally will not charge the condenser to as high a voltage as the selenium type due to the fact that cold cathode rectifiers cease to function at the low currents, which occur when the condensers approach full charge. Both the mercury and high vacuum type rectifiers generally require additional power from the battery to heat their cathodes. Therefore, from the standpoint of eificiency, economy, and performance the selenium type rectifier is preferred.

The number and capacitance of the main storage condenser 26 may be changed without altering the mode of operation of the blasting machine of the invention. Such condensers may be connected in parallel, in series, in series-in-parallel, or in parallel-in-series. Electrolytic condensers are preferred since they combine high capacitance with low weight and small physical size. Other types of condensers such as paper, oil, mica, or ceramic types may be substituted.

The breakdown tube employed in accordance with the invention will have at least three electrodes surrounded by an ionizable gas. The potential at which a particular tube will break down is determined largely by the distance separating the electrodes and the nature and pressure of the gas. Tubes containing more than three electrodes may be employed, but the extra electrodes do not enter into the operation of the machine.

The firing switch could be connected in ways other than that shown in Fig. 1 without changing the overall mode of operation of the blasting machine disclosed. However, the connection employed in the drawing is preferred since it avoids the passing of large firing currents through the switch itself.

Blasting machines built in accordance with the invention are safer to operate and more reliable in performance than any other condenser type, battery operated units available. If a 6-volt battery is employed as an input, the maximum voltage present in the unit when not in operation is 6 volts. Due to the presence of the triggering circuit and breakdown tube, it is impossible to discharge the condensers into the firing line accidentally or prior to their becoming fully charged. Machines in accordance with this invention are light in weight and readily portable. With a 6-volt battery as an input, firing voltages of 500 volts are readily obtainable. Such voltageshave made it possible for machines in accordance with this invention to fire more than 2000 initiators in a single shot.

Since various modifications of the machine disclosed will occur to those skilled in the particular art without departing from the scope of the invention as disclosed, it is intended that the invention shall be limited only by the scope of the appended claims.

What we claim and desire to protect by Letters Patent 1. A blasting machine having in combination an input consisting of a source of low voltage D. C., means associated with the input to interrupt the D. C. comprising a reed vibrator, a charging switch connecting input and vibrator to the primary of a step-up transformer, a rectifier connected to the secondary of the transformer, a con denser connected across the output terminals of the rectifier, a firing switch in its operated position connecting the condenser to an output through a triggering circuit anddisconnecting the D. C. source from the step-up transformer, said triggering circuit comprising an interstage step-up transformer having an adjustable resistance c0nnected across its secondary and a breakdown tube, said breakdown tube having a breakdown voltage higher than the maximum voltage to which the condenser can be charged.

2. A blasting machine in accordance with claim 1 in which a gas-filled glow tube is connected across the condenser.

3. A blasting machine in accordance with claim 1 in which the rectifier consists of at least one rectifier tube.

4. A blasting machine in accordance with claim 1 in which the rectifier is a selenium bridge rectifier connected across the secondary of the transformer.

5. A blasting machine having in combination a D. C. input, a reed vibrator connected to the D. C. input, a voltage multiplying means connected to the vibrator, a charging switch and a firing switch, said input and vibrator being connected to the voltage multiplying means when-the-charging switch isclosed and the firing switch is open; a rectifienconnected to-the-secondary-coil of the volt-agenmltiplyingmeans; at least one condenser connected in-parallel{with the outputof the rectifier, a. stepuptransformer connected to the" condenser when the firing switehis in closed-position anda triode breakdown tube havingabrcakdown-voltage higher than the maximu-rrrvoltage-to-whichthe condenser can be charged,- one electrode of which is connected to the firing switch,. a second*elect-rode--ofwhich is connected'ot'the output of the-step up transformer having an; adjustable resistance connected-across its secondary, and a third electrode of whichis connected to'the outputofthe'machine, the output 'oft the step-up transformer causing breakdown of the breakdown tube" and permitting direct discharge of-th'e'condensenthrough the breakdown tube to the out put of the machine.

6; A blasting machine having incombination an input consisting of a" source oflow voltage D'..C., means associatedwith the input-to interrupt the D. C. comprising a reed vi'brator, a' charging switch connecting input and.

vibrator-to the primary of a step-up transformer, a selenium bridge rectifier connectedrto the secondary of the transformer; a. condenser connected across the output terminalsoftherectifier, a gas filled glow tube connected across the condenser to' indicatethe charge thereof, a firingswitch in its operating position connecting the condenser to anoutput through a triggering circuit and disconnecting the D. C. source from the step-up transformer having an adjustable resistance connected across itssecondary, said triggering circuitcomprising an interstage step up transformer andabreakdown tube, said breakdown tube having a breakdown voltage higher than the maximum voltageto which the condenser can be charged;

7. A blasting'machine in accordance with claim 5 in which a coupling condenser andfaresistorare connected. between.the condenser and the interstage transformer,

said resistor allowing only lirn-itedvD. C; flow there-- through.

8. A blasting machine in accordance with claim.5"in which a resistor equipped'with an adjustabletap is connected across the output of the interstage, transformer and a condenser is connected'between said resistor and ing a .breakdown'voltage. higher than the maximum'voltage to which the storage condenser can be charged.

10. In a condenser-type blasting machine, a triggering circuit connected Jbetweenthe-storage. condenser ancl-xoutput which comprises an interstage step-up transformer, a coupling condenser and resistor connected between the storagecondenser and step-up transformer, a breakdown tube; and a resistor and a condenserconnectedbetween'thestep-up transformer and the breakdown tube, said breakdown tube having: a: breakdown voltage higher'than the maximum voltage to which thestorage=condenser can becharged.

References Cited in'the file of; thispatent UNITED STATES PATENTS Wengel t Jan. 24, 1950 Henninger July 25, 1950 Parker; Aug. 5:, 1952 

